"Mangroves are trees that live in shallow water and provide a fascinating environment," said Dr Mumby, from Exeter University's School of Biological and Chemical Sciences.

"However, these swamps have their fair share of biting insects, crocodiles and snakes. In other words, they are thought to be no great loss when there are local pressures to build shrimp farms, new houses or tourist resorts.

"Everyone sees the point in preserving coral reefs and the creatures that live on them because they are beautiful. Until now, the conservation of mangroves has received much less support."

Urgent action

Mumby's team tells Nature that mangrove forests are an important staging post for the fish as they journey from seagrass beds to their eventual adult habitat.

The fish spend much of their early life seeking food and shelter among the roots of mangroves. Only when the fish are big enough to survive in open water do they swim out to spend their days in and around the coral.

MANGROVE FORESTS

The trees and shrubs grow on tidal wetlands in the tropics

The plants are highly adapted to their salty environment

They help protect the shoreline, seagrass beds and coral reefs

The forests give food and sanctuary to marine lifeforms

But the new study shows that without the mangroves, the fish will often migrate to reefs before they are fully grown, making them more vulnerable to predation.

The Exeter-led team found coral reefs teemed with nearly twice as many snappers (Lutjanus apodus) and grunts (Haemulon sciurus) where healthy mangrove forests were found nearby.

Significantly, the destruction of mangroves may have caused local extinction of one of the largest herbivorous fish in the Atlantic - the rainbow parrotfish (Scarus guacamaia).

"The snapper is the fish you are most likely to eat on your Caribbean holiday - it's the 'cod of the Caribbean'. But it will cease to be common if we continue to destroy its habitat.

"Urgent action needs to be taken to preserve mangroves if Caribbean fisheries and coral reefs are to be preserved."